Although metal pulleys have been common as pulleys used in the vicinities of engines of automobiles or the like, the substitution of the metal pulleys for resin pulleys has been examined with recent requests to make automobile parts small, lightweight, and low in cost.
Particularly, a resin pulley using a phenol resin as a base resin, and obtained by reinforcing the phenol resin by a reinforcing fiber and curing the phenol resin simultaneously with or after molding has good dimensional stability and strength which are approximately the same as those of the metal pulley.
However, the wear resistance of the resin pulley is liable to be reduced as the content of the reinforcing fiber is increased in order to improve such dimensional stability and strength. The resin pulley is liable to wear away when it is brought into contact with raised dust or the like, particularly in a dust atmosphere in cases such as a case where the automobile travels on an unpaved road as the wear resistance is reduced. Therefore, the wear resistance of the resin pulley may not be sufficient, as compared with that of the metal pulley.
Accordingly, various types of attempts have been made to put a resin pulley having superior properties which can be used as an alternative to the metal pulley to practical use.
For example, Japanese Laid Opened Patent Application No. 08-159244 (1996) suggests forming a resin pulley of a resin composition obtained by adding to a phenol resin, a mica powder, a glass fiber and at least one type of inorganic powder selected from a group consisting of calcium carbonate, clay, and wallastonite, to improve the wear resistance of the resin pulley.
However, both the inorganic powder and the mica powder, as illustrated, are soft. Accordingly, each of the powders itself is liable to wear away by coming into contact with the dust or the like particularly in the above-mentioned dust atmosphere. Further, respective fine powders of the inorganic powder and the mica powder which have worn away to drop out of the resin pulley, together with the dust, promote the wear of the resin pulley. Therefore, the wear resistance of the resin pulley is rather reduced.
Japanese Patent Publication No. 3192082 suggests forming a resin pulley of a resin composition obtained by adding to a phenol resin an inorganic fiber, an organic fiber, a silica powder, and an elastomer, to improve the wear resistance of the resin pulley.
The silica powder is harder than the inorganic powder and the mica powder, previously described. Accordingly, the improvement of the wear resistance of the resin pulley in the dust atmosphere or the like is expected.
However, the content of the silica powder is as low as 3 to 7% by weight to the total amount of the resin composition. Moreover, the resin composition contains a soft organic fiber and an elastomer. Accordingly, the effect of improving the wear resistance of the resin pulley in the dust atmosphere or the like is also insufficient.